1. Field of the Invention
This invention relates generally to a method and apparatus for increasing platform attitude adjustment range for platforms supported by jacks of a given stroke length.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
There are a wide variety of commercial and industrial applications requiring mobile platforms that can be aligned relative to Earth's gravity (true level) by a known angle, or set of angles. The platforms are mobile and are often self-propelled, allowing them to be easily moved to various locations on the Earth's surface. However, once at a given location the platform must be supported and aligned relative to Earth's gravity before operating in its intended capacity. Examples of such platforms include: heavy industrial equipment, cranes, cherry pickers, and recreational vehicles.
The support and alignment of the platform is often accomplished through the use of jacks attached at different positions around the platform. The jacks may be extended to contact the ground, creating a rigid support base for the platform. By extending and retracting specific jacks, the platform may be aligned to at any angle allowed within the mechanical limits of the platform and jacks. The jacks may be hydraulically driven, or may be driven by DC electric motors.
With the advent of these platforms came the need for systems that can control jack movement (extension and retraction) and automate the task of bringing a platform to a known desired attitude. (Although, in the art, these systems are sometimes referred to as “mobile platform automatic positioning systems”, this document will refer to them as mobile platform automatic attitude adjustment systems, or just “platform attitude adjustment systems” for short. This is because the word “positioning” has connotations more closely related to translation of a body through space rather than the adjustment of the attitude of a body “in-place.” This document uses the word “system” to refer simultaneously to both an apparatus and a process (or method) carried out by that apparatus.)
Recent improvements in sensor technology, combined with the falling prices of semiconductors and microprocessors, are advancing the state-of-the-art in platform attitude adjustment systems. Where, in the past, jack movement was coordinated through the use of discrete circuitry and limited feedback, today it is known for computer processors to use new sensor technologies and advanced algorithms to adjust platform attitudes faster, safer, and more accurately than before. Today's systems are several orders of magnitude more sophisticated and powerful than their predecessors, allowing for unprecedented levels of control and reliability in their operation, but are configured to operate only hydraulically-actuated jacks.
When using jacks to adjust the attitude of a platform, the platform's total range of motion depends mainly on the distance between the jacks, and the total stroke lengths of the jacks. A platform attitude adjustment system cannot position or change the attitude of a platform beyond the point where all jack stroke has been used up.
The diagrams shown in FIGS. 1 and 2 schematically illustrate the basic relationship between platform position and jack stroke in a simplified two-jack system in which one jack extends or retracts while the other jack remains stationary. In such systems a stationary pivot point of the platform is located at the stationary jack. In most applications there are at least four jacks supporting a platform in spaced locations, e.g., near each of the four corners of a generally rectangular platform. However, for the sake of simplicity, as with FIGS. 1 and 2, this document will address the operation of the attitude adjustment system with respect to only two adjacent jacks.
The following parameters are used to trigonometrically describe the total attitude adjustment capability of a platform positioning system:                h=maximum stroke of jack        w=distance between any two jacks        
If one jack uses up its entire stroke and the other remains stationary, the largest angle (θ) through which the platform may be tilted in the axis of the two jacks is calculated using the following equation:
  θ  =            tan              -        1              ⁡          (              h        w            )      
When designing a platform attitude adjustment system, the jack stroke and placement must be carefully chosen to ensure that the system can move a supported platform through a desired range of attitudes. In most mobile platform attitude adjustment applications, the amount of distance between supporting jacks depends primarily on platform geometry and is not likely to be adjustable. The only variable a designer is generally free to modify with regard to the selection and arrangement of jacks for a given mobile platform application is in the stroke lengths of the jacks. To reduce the cost of the jacks in a platform attitude adjustment system, jacks should be selected that have the shortest stroke lengths possible. However, the jack stroke lengths must be long enough to ensure that the jacks are able to move the platform through a predetermined desired range of attitudes.
It is known for mobile platform automatic attitude adjustment systems to include controllers programmed to coordinate jack movement. For example, U.S. Pat. No. 5,143,386 issued 1 Sep. 1992 to Uriarte, discloses a mobile platform attitude adjustment system that includes a plurality of jacks supporting a platform and powered by respective electric jack motors. A controller is connected to each of the jack drive mechanisms and is programmed to adjust the attitude of the platform by controlling the operation of the jacks. The controller of the Uriarte system is further programmed to coordinate the operation of the jacks as the jacks are adjusting the attitude of the platform. More specifically, the controller adjusts individual jack speeds in accordance with which part of the platform is lowest. However, a mobile platform attitude adjustment system constructed according to the Uriarte patent is unable to increase the range of attitudes through which a platform can be adjusted for a given jack stroke length.
What is needed is a mobile platform attitude adjustment system that coordinates jack actuation in such a way as to increase the range of attitudes through which a platform can be adjusted for a given jack stroke length. This would allow jacks of a shorter stroke length to be selected when designing or adapting a mobile platform attitude adjustment system to suit a given application.